Double grating monochromator optical design of the pure rotational Raman-lidar

The temperature of troposphere is an important meteorologic parameter, the pure rotational Raman-lidar technique has already used on effective temperature-measuring of troposphere at present. Because many low-intensity scattering is around high-intensity scattering, it is difficult to acquire Raman spectrum from high-intensity Mie+ Rayleigh scattering. So the prismatic system needs reach high capability. The double grating monochromator for a pure rotational Ramanlidar can provide better than 10-7 suppression of spectral line due to unshifted Mie+ Rayleigh scattering, obtain highpurity rotational Raman spectrum, and improve transmission and stability of the optical system. The complex structure of the double grating monochromator is always difficult to Raman-lidar. Two optical paths of grating are compared and a conclusion can be drawn that the structure of beam path of grating of symmetrical arrange of optical fibre is better in grating efficiency than the structure of beam path of grating of linear arrange of optical fiber. Then a formula about relative of range of diffractive angle and order of grating is obtained through grating equation and rotational Raman equation. When grating constant is 600 line/mm, the fifth order of grating is optimal. According to these, we can optimize the double grating monochromator from the paths of grating and parameter of grating and improve transmission and stability of lidar temperature-measuring system, make the whole lidar system higher Signal-to-Noise, and attain more exact atmosphere outline.